Magnetic brush development apparatus utilizing magnetic means

ABSTRACT

Magnetic brush developing apparatus for developing a latent image on a moving insulating layer with magnetic developer, the apparatus comprising first magnetic means having a longitudinal axis extending substantially parallel to the moving, latent image bearing layer and substantially transverse to the direction of movement thereof, the first magnetic means having only one plane of polarization which is directed substantially transverse both to the longitudinal axis and the moving, latent image bearing layer to produce a first magnetic field at the layer, means for moving the magnetic developer through the first magnetic field to initiate development of the latent image, second magnetic means having a longitudinal axis extending substantially parallel to the moving, latent image bearing layer and substantially transverse to the direction of movement thereof, the second magnetic means being subsequent to the first magnetic means along the direction of movement of the image bearing layer and being polarized at a plurality of predetermined angles about the longitudinal axis where, at each angle, the second magnetic means is polarized in a direction substantiallly transverse to the longitudinal axis to thereby produce a plurality of magnetic fields at the layer, means for transferring the magnetic developer from the first magnetic field produced by the first magnetic means to the plurality of magnetic fields produced by the second magnetic means to continue and complete the development of the latent image, the second magnetic means compensating the tendency of the rectangular magnet to underdevelop the latent image portions adjacent the end portions of the first magnetic means and the first magnetic means compensating the tendency of the second magnetic means to nonuniformly develop the latent image.

United States Patent Okada 1 1 MAGNETIC BRUSH DEVELOPMENT APPARATUS UTILIZING MAGNETIC MEANS [75] Inventor: Ryuzo Okada, Yamato, Japan [73] Assignee; Fuji Xerox Co., Ltd., Tokyo. Japan [22] Filed: Jan. 25, 1974 1211 Appl. No.: 436,713

Primary E.\aminer-Mervin Stein Assistant Examiner-Douglas Salser Attorney, Agent, or Firm-Gerald .l. Ferguson, Jr.; Joseph J. Baker [57] ABSTRACT Magnetic brush developing apparatus for developing a latent image on a moving insulating layer with magnetic developer, the apparatus comprising first mag- 1 1 Sept. 30, 1975 netic means having a longitudinal axis extending substantially parallel to the moving, latent image bearing layer and substantially transverse to the direction of movement thereof, the first magnetic means having only one plane of polarization which is directed substantially transverse both to the longitudinal axis and the moving, latent image bearing layer to produce a first magnetic field at the layer, means for moving the magnetic developer through the first magnetic field to initiate development of the latent image, second magnetic means having a longitudinal axis extending substantially parallel to the moving, latent image bearing layer and substantially transverse to the direction of movement thereof, the second magnetic means being subsequent to the first magnetic means along the direction of movement of the image bearing layer and being polarized at a plurality of predetermined angles about the longitudinal axis where, at each angle, the second magnetic means is polarized in a direction substantiallly transverse to the longitudinal axis to thereby produce a plurality of magnetic fields at the layer, means for transferring the magnetic developer from the first magnetic field produced by the first magnetic means to the plurality of magnetic fields produced by the second magnetic means to continue and complete the development of the latent image, the second magnetic means compensating the tendency of the rectangular magnet to underdevelop the latent image portions adjacent the end portions of the first magnetic means and the first magnetic means compensating the tendency of the second magnetic means to nonuniformly develop the latent image.

2 Claims, 3 Drawing Figures U.S. Patent Sept. 30,1975 3,908,595

FIG. I (PRIOR ART) FIG. 2

FIG. 3

MAGNETIC BRUSH DEVELOPMENT APPARATUS UTILIZING MAGNETIC MEANS BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a developing apparatus in a copying machine, and more particularly to magnetic brush developing apparatus using a plurality of magnetic brush rolls in a dry type high-speed copying machine.

2. Discussion of the Prior Art The so-called magnetic brush development, along with cascade development is a particularly popular method of development in a dry type copying machine. Generally, the magnetic brush method is preferred for obtaining better reproducibility of wide-area images in a high-speed copying machine.

Generally, in the magnetic brush developing process, the peripheral speed of the photosensitive plate is increased with increased copying speed. Thus, in order to obtain reproductions with satisfactory image density, it has been necessary either to increase the peripheral speed of the magnetic brush rolls or to increase the number of such rolls used. However, if the peripheral speed of the magnetic brush rolls is increased too much, the developer powder is blown off the periphery of each roll by centrifugal force or it slips on the roll surfaces. Also, scattering of the toner particles into the air is promoted thus soiling the background portion of the copying paper or the inside of the copying machine. Therefore, to alleviate this problem and to obtain reproductions with high image quality, it has been necessary to use a plurality of magnetic brush rolls disposed along the periphery of the plate to keep the peripheral speed of each roll below a certain level,

To facilitate transfer of the developer from roll to roll as well as removal of the developer from the rolls, it is preferable that each of the magnetic brush rolls comprises a magnet fixed with a certain orientation and a cylindrical body rotatably disposed around the magnet. The magnets used in such magnetic brush rolls may be roughly divided into the following two types in terms of shape.

One type is the rectangular prismatic magnets which have a magnetization pattern directed toward the sensi tive plate, and the other type is the cylindrical or columnar magnets which are magnetized to provide more than two poles on the magnet surface.

However, in a magnet assembly composed of a combination of rectangular prismatic magnets, each magnet provides magnetism on both the front and back sides so that the magnetic lines of force at both ends of each magnet are directed opposite to that of the circular field in the middle of the magnet. That is, magnetic lines of force at the ends present a pattern such as indicated by a in FIG. 1 and these tend to be oppositely directed to those at the middle of the magnet. This means that the density of developer is high at the end areas of the roll surface of each magnet, and hence, rise-up of the developer at such areas is low. That is, the developer does not tend to rise up from the roll surface. Thus, the image density at the end areas of each magnet is lower than the density in the middle portion thereof. Hence, it is necessary to make the magnet length substantially greater than the width of the copy paper. This necessarily enlarges the size of the copying machine and increases manufacturing cost.

Also, when a number of magnetic brush rolls having magnet assemblies composed of combinations of rectangular prismatic magnets are employed, it has been confirmed, although the reason is not known, that the effective developer flow area is narrowed when the developer is transferred from one roll to the other.

When cylindrical or columnar magnets are employed, the problems attendant with the use of rectangular prismatic magnets are lessened and uniform density development can be effected with magnets of relatively short length. In this case, however, as compared with rectangular prismatic magnets, there is a tendency for the developer rise-up area to narrow and for the rise-up height to be low. Therefore, the space between the photosensitive plate and the magnetic brush roll surface greatly affects the image quality. Further, deflection of the'photosensitive plate or the magnetic brush rolls causes variation of image density, and thus high accuracy is required for setting the developing mechanism.

SUMMARY OF THE INVENTION A primary purpose of the present invention is to provide an improved developing apparatus in a copying machine where the aforementioned problems of the prior art are overcome.

Other objects and advantages of this invention will become apparent upon reading the appended claims in conjunction with the following detailed description and the attached drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a diagrammatic illustration of a pattern of magnetic lines of force produced by a rectangular prismatic magnet.

FIG, 2 is a schematic drawing of an illustrative embodiment of the present invention.

FIG. 3 is a sectional view taken along the line III-lII of FIG. 2.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT In the drawings, a sensitive drum 1 is illustrated, the surface of which is subjected to electric charging and exposure by a method generally known as the xerography process, so as to form thereon electrostatic latent images. A developing mechanism 2 is provided in opposition to the surface of the sensitive drum 1 for developing the electrostatic latent images on the drum surface. Developing mechanism 2 comprises three magnetic brush developing rolls 3, 4 and 5, a toner distributor 6, a developer guide plate 7, a developer stirring means 8, and a developer flow rate regulator plate 9.

Each of the magnetic brush developing rolls 3, 4 and 5 includes at least one magnet (which are described in more detail below) and a preferably non-magnetic cylinder disposed for clockwise rotation about its associated magnet or magnets. A pair of rectangular prismatic magnets 13 and 14 are fixedly disposed in rotatable cylinder 10 of magnetic brush developing roll 3, and cylindrical magnets 15 and 16 are respectively fixedly disposed in rotatable cylinders 11 and 12 of rolls 4 and 5, and these magnets are secured to fixed rods 17, 18 and 19, respectively.

In operation, the developer is supplied from a space between the cylinder 10 of the lowermost magnetic brush developing roll 3 and the developer flow rate regulator plate 9 by the attraction of magnets 13 and 14 for the developer and is moved forward in the magnetic field of these magnets with rotation of cylinder 10 to initiate development of the latent image on drum 1. It is subsequently transferred to rolls 4 and 5 as image development continues. The used developer separates from the topmost magnetic brush developing roll 5 and flows down over developer guide plate 7.

The used developer with reduced toner content is replenished with toner from toner distributor 6. The toner-replenished developer falls through double-layer de veloper stirring means 8. One of the layers in stirring means 8 moves the developer forwardly in FIG. 2 and the other layer moves it rearwardly in FIG. 2, to thereby provide a uniform toner distribution in the developer and to maintain an optimum pattern of electric charging of both toner and carrier.

FIG. 3 is a view along the line lIIIII of FIG. 2. As will be seen in the figure, the cylinders l0, l1 and 12 are rotated by their respective driving shafts 20, 21, and 22, and the magnets are secured to the fixed rods l7, l8 and 19, respectively, which are, in turn, secured to a side wall 26 of the housing through securing means 23, 24 and 25, respectively. The broken slant lines in FIG. 3 show the pattern of developer. According to results of experiments, it was confirmed that developer on the magnetic brush developing rolls has the following features. Rise-up of developer is high and a satu rated state of coarse developer is created at part I? in FIG. 3, but such tendency is diminshed in parts L and (I, and that the range of uniform deposition of the developer is relatively narrow at part b and wider at parts c and (I.

The developing apparatus according to the present invention, as described above, comprises magnetic brush developing rolls using cylindrical or columnar magnets and a magnetic brush developing roll using a pair ofjoined rectangular prismatic magnets, the magnets being arranged so that the high rise-up of devel oper caused by the rectangular prismatic magnets will help to reduce non-uniformity of image density caused by deflection of the developing rolls and sensitive plate as is the case in conventional developing systems, while the cylindrical or columnar magnets effect uniform development along the width of the copying paper, thus making it possible to obtain uniform image quality with a relatively simple structure.

While the present invention has been described by way ofa preferred embodiment thereof, it is not limited to this particular embodiment. For example, the direction of rotation of the sensitive plate or the direction of flow of the developer can be selected freely to suit the situation, and hence the additional use of a developer lifting mechanism is involved within the technical scope of the present invention. Also, the number of magnetic brush developing rolls is not limited to three as in the shown embodiment but any number of such rolls, if not smaller than two, can be used as is necessary. Further, it is not essential to use cylindrical or columnar magnets; it is possible to use magnets of other configurations if they are capable of forming a mag netic flux distribution equivalent to the multipole magnetization pattern formed on the surface of a cylindrical or columnar magnet. A similar flux distribution can be also obtained by using many rectangular prismatic magnets.

Numerous modifications of the invention will become apparent to one of ordinary skill in the. art upon reading the foregoing disclosure. During such a reading it will be evident that this invention provides unique magnetic brush development apparatus for accomplishing the objects and advantages hereinstated.

What is claimed is:

1. Magnetic brush developing apparatus for developing a latent image on a moving insulating layer with magnetic developer, said apparatus comprising a rectangular magnet having a longitudinal axis extending substantially parallel to said moving, latent image bearing layer and substantially transverse to the direction of movement thereof. said rectangular magnet having only one plane of polarization which is directed substantially transverse both to said longitudinal axis and said moving, latent image bearing layer to produce a first magnetic field at said layer;

means for moving said magnetic developer through said first magnetic field to initiate development of said latent image;

at least one cylindrical magnet having a longitudinal axis extending substantially parallel to said moving. latent image bearing layer and substantially transverse to the direction of movement thereof, said cylindrical magnet being subsequent to said rectangular magnet along the direction of movement of said image bearing layer and being polarized at a plurality of predetermined angles about said longitudinal axis where, at each angle, said cylindrical magnet is polarized in a direction substantially transverse to said longitudinal axis to thereby pro duce a plurality of magnetic fields at said layer; means for transferring said magnetic developer from said first magnetic field produced by said rectangular magnet to said plurality of magnetic fields produced by said cylindrical magnet to continue and complete the development of said latent image; said cylindrical magnet compensating the tendency of said rectangular magnet to underdevelop the latent image portions adjacent the end portions of the rectangular magnet and said rectangular magnet compensating the tendency of said cylindrical magnet to nonuniformly develop the latent image.

2. Apparatus as in claim 1 where both said moving means and said transferring means comprise rotatable, hollow cylinders concentric with said first and second magnetic means respectively. 

1. Magnetic brush developing apparatus for developing a latent image on a moving insulating layer with magnetic developer, said apparatus comprising a rectangular magnet having a longitudinal axis extending substantially parallel to said moving, latent image bearing layer and substantially transverse to the direction of movement thereof, said rectangular magnet having only one plane of polarization which is directed substantially transverse both to said longitudinal axis and said moving, latent image bearing layer to produce a first magnetic field at said layer; means for moving said magnetic developer through said first magnetic field to initiate development of said latent image; at least one cylindrical magnet having a longitudinal axis extending substantially parallel to said moving, latent image bearing layer and substantially transverse to the direction of movement thereof, said cylindrical magnet being subsequent to said rectangular magnet along the direction of movement of said image bearing layer and being polarized at a plurality of predetermined angles about said longitudinal axis where, at each angle, said cylindrical magnet is polarized in a direction substantially transverse to said longitudinal axis to thereby produce a plurality of magnetic fields at said layer; means for transferring said magnetic developer from said first magnetic field produced by said rectangular magnet to said plurality of magnetic fields produced by said cylindrical magnet to continue and complete the development of said latent image; said cylindrical magnet compensating the tendency of said rectangular magnet to underdevelop the latent image portions adjacent the end portions of the rectangular magnet and said rectangular magnet compensating the tendency of said cylindrical magnet to nonuniformly develop the latent image.
 2. Apparatus as in claim 1 where both said moving means and said transferring means comprise rotatable, hollow cylinders concentric with said first and second magnetic means respectively. 